Yea you can as long as you don't preform any tricks that a normal controller can't, as far as I'm aware of

^ correct

Be sure to disable left+right on the emulator you are using.

You can use keyboard. Rules can be access by clicking the "View Rules" button on the leaderboard.

I think it's time I make an FAQ post to address some of these questions.

pepega

Not sure how you would use a mouse to play SMB but yes